Electrolytic preparation of reduced



Feb. 14, 1956 T, M. BUCK ETAL 2,734,355

ELECTROLYTIC PREPARATION OF REDUCED TITANIUM CHLORIDE COMPOSITION FiledNov. 20. 1951 Fig. I.

INVENTQRS Thomas M. Buck BY Marshall B. Alpert United States fiatentELECTROLYTIC PREPARATION OF REDUCED TITANIUM CHLORIDE COIWPOSITIONThomas M. Buck, Plainfield, N. J., and Marshall B. Alpert, StatenIsland, N. Y., assignors to National Lead Company, New York, N. Y., acorporation of New Jersey Application November 20, 1951, Serial No.257,258

3 Claims. (Cl. 204-61) This invention relates to a method for preparingreduced titanium chloride compositions. More specifically it relates toan electrolytic method for preparing reduced titanium chlorides.

Reduced titanium chlorides, that is, titanium dichloride and titaniumtrichloride are powerful reducing agents. Titanium dichloride inparticular finds commercial use as a reducing agent in many non-aqueousorganic and inorganic systems.

Several methods are known for preparing reduced titanium chlorides. Forexample, titanium tetrachloride may be reduced to titanium dichlorideor' titanium trichloride by reaction with a metallic reducingagent suchas sodium or magnesium. Small amounts of titanium dichloride andtitanium trichloride have also been produced by passing titaniumtetrachloride over titanium metal. Apparently however, the titaniummetal soon becomes coated with a portion of the reduced titaniumchlorides and further reaction between the titanium tetrachloride andtitanium metal is hindered.

An object of this invention, therefore, is to provide a direct methodfor preparing reduced titanium chloride compositions. A still furtherobject of the instant invention is to provide an electrolytic processfor the preparation of compositions containing titanium dichloride andtitanium trichloride. Another object of this invention is to provide asimple and economical electrolytic method for the preparation of reducedtitanium chloride compositions in which the compositions contain largeamounts of titanium dichloride and small amounts of titaniumtrichloride. These and other objects will become apparent from thefollowing more complete description of the instant invention.

Broadly this invention contemplates a method for preparing reducedtitanium chloride composition which comprises employing, in anelectrolytic cell having an anode, a cathode, and a molten saltelectrolyte titanium metal as the anode in said cell, and introducingtitanium tetrachloride into the cell, meanwhile concurrently passingelectricity through said electrolytic cell in amount sufficient toconvert all of the titanium tetrachloride to reduced titanium chloride,whereby an electrochemically equivalent amount of titanium metal fromthe anode is solubilized during the conversion of titanium tetrachlorideto reduced titanium chloride.

In order to more clearly illustrate the type of apparatus which has beensuccessfully used in preparing reduced titanium chloride compositionsaccording to the instant invention, Fig. l and Fig. 2 are presented inwhich Fig. 1 shows in cross-section a type of electrolytic cell which issuitable for employment and Fig. 2 shows, also in crosssection, a typeof anode which may also be used in place of the anode shown in Fig. l.

Referring to Fig. l, the electrolytic cell consists of container 11which is heated externally by gas flames 12, in furnace 13. The halidesalt electrolyte 14 is placed in the container 11 and a cathode 15 isinserted into the cell and extends down into the electrolyte. Thecathode may ice be composed of any suitable material such as nickel. Theanode 16 consists of titanium metal from which a portion of the reducedtitanium chloride is obtained as the process progresses. In thisparticular instance the cathode is made up of a hollow nickel tubethrough which titanium tetrachloride may be introduced into theelectrolytic cell. However, the titanium tetrachloride may be introducedinto the electrolyte through a separate inlet port positioned adjacentto the cathode, and the cathode may'possess other suitable form as forexample, that of a solid rod or bar. The cell is further provided with avent 17 through which any gaseous products may be removed.

The particular type of anode construction is unimportant andsubstantially any suitable means for supporting the anodic titaniummetal may be utilized. For instance, the titanium metal may beconsolidated such as by sintering or pressing into the form of a rod orbar which is then immersed into the fused salt bath as the anode.Another method of suspending the impure titanium metal in the fused saltbath is to provide a metallic container such as a basket, for example,one constructed of nickel or other suitable material in which thetitanium metal may be placed. A suitable basket type anode 16Acontaining lumps of impure titanium metal 18 is shown in Fig. 2.

The amount of fused halide salt electrolyte originally present in theelectrolytic cell is not critical and may be present in amount only tobe sufiicient to permit initiation of the electrolysis reaction. Thestarting halide salt electrolyte preferably is composed of at least onecompound selected from the group consisting of the halide salts of thealkali metals, alkaline earth metals and magnesium. It is particularlydesirable to employ the chlorides of said metals because of theeconomics involved. These halides may be employed singly or incombination. Mixtures of these halides which form low melting pointeutectics are most convenient to employ, such as mixtures of sodiumchloride and strontium chloride or sodium chloride and magnesiumchloride.

The temperature of operation may also vary over a considerable range.Naturally it is necessary to employ temperatures sufliciently high tomaintain the reduced titanium chloride composition in the molten stateduring electrolysis. The use of exceedingly high temperatures isundesirable because of the increased tendency toward corrosion andattack on the equipment involved. An atmosphere of argon or other inertgas is preferably maintained above the molten salt bath in order toprevent contamination of the titanium values by the outside atmosphere.

In order to carry out the process of the instant invention, the titaniummetal employed as the anode is introduced into the fused salt bath.Titanium tetrachloride is then introduced into the fused salt bath inthe vapor state and a sufficient quantity of electricity is concurrentlypassed through the electrolytic cell in order to reduce the titaniumtetrachloride substantially immediately to titanium dichloride andtitanium trichloride. At the same time an electrochemically equivalentamount of the titanium metal at the anode is dissolved to form anadditional amount of reduced chlorides.

To prepare reduced titanium chloride compositions according to theinstant invention, it is desirable theoretically to pass approximatelyfrom 1 to 2 faradays of electricity through the cell for each mol oftitanium tetrachloride introduced. 'In actual practice a quantity ofelectricity slightly in excess of the theoretical amount is usuallyemployed in order to overcome current losses due, for example, to sidereactions and other effects occurring as a result of the particular celldesign which is employed. If one desires to prepare reduced titaniumchloride compositions containing a large proportion of titaniumdichloride, it is preferred in theory to add electricity in a quantityequivalent to. approximately 2. faradays per mol of titaniumtetrachloride introduced. In practice, high titanium dichlorideconcentrations have been obtained by passing through the cell from about1.8 to 2.3 faradays per molv of titanium tetrachloride.introduced. Inactual practice the extended use of electricity in excess of 2.3faradays per mol of titanium tetrachloride introduced, results in; partof the titanium values depositing as titanium metal on the cathode. If,one, addsless than. 1.8 faradays per mol of titanium tetrachlorideintroduced, the reduced chloride composition will contain largerproportions of titanium trichloride. As stated above for each mol oftitanium tetrachloride converted to reduced titanium chlorides, it hasbeenfound: that an electrochemiv callyequivalent amount oftitaniummetalfrom the anode will also be convertedto reduced titanium chlorides.Thus, in theory, when approximately Z'faradays of electricity per mol oftitanium tetrachloride introduced are passed through the cell,substantially one mol of titanium metal will likewise be converted toreduced chloride. Obviously, if less than 2 faradays per mol of titaniumtetrachloride introduced is used, a proportionally smaller amount oftitanium metal from the anode will be solubilized.

In carrying out the process of the instant invention, titaniumtetrachloride is introduced into a cell having a titanium-metal anode,and concurrently a quantity of electricity in amount sufiicient toreduce the titanium tetrachloride to reduced titanium chloride is passedthrough the cell, and as the process is continued the reduced titaniumchloride composition is steadily enriched. At any concentration thereduced titanium chloride composition may be removed from theelectrolytic cell and solidified as by cooling, and the resultantproduct will'be in such form as to be conveniently handled or stored.

In order to illustrate further the process. of the instant invention thefollowing. examples are presented:

Example 1 Using an electrolytic cell as described in Fig. l, thefollowing experiment was conducted in order to prepare a mixture ofreduced titanium chloride composition.

10,000 grams of a chloride. salt electrolyte consisting of 7,300 gramsof strontium chloride and 2,700 grams of sodium chloride were placed ina cell and heated to 700 C., a hollow nickel cathode wasinserted intothe fused salt bath. An anode consisting of impure titanium. metal wasalso inserted into theelectrolyte. Titanium tetrachloride vapors werethen added at the rate of 2.9 grams per minute through the hollow nickelcathode. Simultaneously electricity equivalent to .2 faradays per mol oftitanium tetrachloride introduced was passed. through the cell byemploying a current of 50 amperes at an impressed voltageofapproximately l.3 volts. The anode current density was approximately0.3. ampere per. square-centimeter, and a cathode current density ofabout-0.2 ampere per square centimeter was maintained. The titaniumtetrachloride and a portion of the impure metal anode were converted tosolubilized titanium dichloride and ti-. tanium trichloride. The processwas continued for 9 hours, the fused salt bath was analyzed and found tocontain concentrations equivalent to 1.2 molal titanium dichloride and0.3 molal titanium trichloride. This product was used as theelectrolytic medium in a process for electrolytically refining impuretitanium metal;

Example 2 Another reduced titanium chloride composition was prepared inwhich higher concentration of the reduced titanium chlorides wasobtained as titanium dichloride. 7300 grams of strontium chloride and2700 grams. of sodium chloride were placed in a cell similarin design tothat described in Fig. .1 and heated to 700 C. Titanium metal was theninserted into the molten-chloride electrolyte 4. as the anode, and ahollow nickel cathode was also placed in the electrolyte. Titaniumtetrachloride vapors were then added at the rate of 2.7 grams per minutethrough the hollow cathode into the electrolyte. Simul- 5 taneouslyelectricity in amount equivalent to 2 faradays per mol of titaniumtetrachloride introduced was passed through the cell. The sameconditions with respect to current and electrode current densities asreported in. Example 1 were. maintained in this example. The'titanium l0tetrachloride and a portion of the impure titanium metal anode wereconverted-to solubilized: titanium dichloride and trichloride. Theprocess was continued for 60 hours and the fused salt mixture then wasremoved from the electrolyticcell. The product was analyzed and found tocontain concentrations equivalent to 8 molal titanium dichloride and 2molal titanium trichloride.

It has clearly been shown by the description and examples presentedabove that reduced titanium chloride compositions maybe directlyprepared according to an electrolytic process in which titaniumtetrachloride is in troduced into an. electrolytic cell having an impuretitanium metal anode and a halide salt electrolyte and in whichelectricity ispassed through the electrolytic cell whereby the titaniumtetrachloride and a portion of the impure titanium metal anode areconverted to reduced titanium chlorides. Furthermore, it has been shownthat it is possible to provide an electrolytic method which is simpleand economical. to operate forthe'preparation of reduced titaniumchloride compositions containing large proportionsof'titaniumdichloride.

While this invention has been described and illustrated by theexamplesshown, it is not intended to be strictly limited thereto and othermodifications and variations may be employed within the scope of thefollowing claims. We claim:

1. Method for the preparation of reduced titanium chloride compositionwhich comprises employing, inan electrolytic cell having a titaniummetal anode, a cathode and a molten salt electrolyte, said electrolytebeing com- 40 posed of at least one compound selected from the groupconsisting of the halide salts of alkali metals, alkaline earth metalsand magnesium, and introducing titanium tetrachloride below the surfaceof said electrolyte adjacent to said cathode,- meanwhile concurrentlypassing electricity through said cell, said electricity and said TiCl-ibeing added in a faraday per mol ratio such as to convert all of thetitanium tetrachloride to titanium trichloride and titaniurn dichloride,whereby an electrochemically equivalent amount. of titanium. metal fromthe anode is solubilized' during the conversion of titaniumtetrachloride to reduced titanium chloride.

2. Method according toclairn 1 wherein the electricity is added inamountfrom 1.8 to 2.3 faradays for each mol of titanium tetrachlorideintroduced into said cell. whereby the titanium trichloride and titaniumdichloride composition comprises predominantly titanium dichloride.

3. Method according. to claim 1 wherein said cathode has a bore andwherein said titanium tetrachloride is introduced into said cell throughsaid bore.

References Cited in the file of this patent UNITED STATES PATENTS723,217 Spence Mar. 17, 1903 FOREIGN PATENTS 615,951 Germany July 16,1935' OTHER REFERENCES Electrolytic OxidationandReduction, by Glasstoncet al.;published in 1936, page 46. 7

Chemical Abstracts, vol. 34 (1940) page 7756, abstractof article by'Sklyarenko et-al.

1. METHOD FOR THE PREPARATIN OF REDUCED TITANIUM CHLORIDE COMPOSITIONWHICH COMPRISES EMPLOYING, IN AN ELECTROLYTIC CELL HAVING A TITANIUMMETAL ANODE, A CATHODE AND A MOLTEN SALT ELECTROLYTE, SAID ELECTROLYTEBEING COMPOSED OF AT LEAST ONE COMPOUND SELECTED FROM THE GROUP METALSAND MAGNESIUM, AND INTRODUCING TITANIUM TETRACHLORIDE BELOW THE SURFACEOF SAID ELECTROLYTE ADJACENT TO SAID CATHODE, MEANWHILE CONCURRENTLYPASSING ELECTRICITY THROUGH SAID CELL, SAID ELECTRICITY AND SAID TIC14BEING ADDED IN A FARADAY PER MOL RATIO SUCH AS TO CONVERT ALL OF THETITANIUM TETRACHLORIDE TO TITANIUM TRICHLORIDE AND TITANIUM DICHLORIDE,WHEREBY AN ELECTROCHEMICALLY EQUIVALENT AMOUNT OF TITANIUM METAL FROMTHE ANODE IS SOLUBILIZED DURING THE CONVERSION OF TITANIUM TETRACHLORIDETO REDUCED TITANIUM CHLORIDE.